A high electron mobility transistor (HEMT) is an example of a conventional power semiconductor device. A HEMT may be fabricated using a III-nitride semiconductor, which, when referred to herein, means a semiconductor alloy from the AlInGaN system such as GaN, AlGaN, InGaN, or the like.
A HEMT according to the conventionally known art includes a first III-nitride semiconductor body, which may be composed of, for example, undoped GaN, and a second III-Nitride semiconductor body, which may be composed of, for example, AlGaN, disposed over first III-nitride semiconductor body. As is well known, the heterojunction of first III-nitride semiconductor body and second III-nitride semiconductor body results in the formation of a conductive region usually referred to as a two dimensional electron gas (2DEG).
A typical HEMT further includes at least two power electrodes. The current is conducted through the 2DEG between the two power electrodes.
A HEMT may also include a gate arrangement which can be operated to disable and enable the 2DEG as desired, thereby turning the device ON or OFF. As a result, a HEMT can be operated like a field effect transistor. Indeed, such a device is sometimes referred to as a heterojunction field effect transistor (HFET).
Due to their low loss, high current carrying and high breakdown voltage capabilities III-nitride-based heterojunction power semiconductor devices are suitable for power applications. However, many III-nitride semiconductor devices are normally ON, which means that a bias to the gate is required to render the device OFF. Normally ON devices are less desirable for power application because: a) such devices are operated less efficiently that normally ON devices; b) the drive circuitry for normally ON device are more complicated and thus more expensive.
It is thus desirable to have a normally OFF III-nitride power semiconductor device.